1) Field of the Invention
The present invention relates to an additive for a starch based adhesive used in the manufacturing of corrugated board. More particularly, present invention is a combination of sodium hydroxide, borax, boric acid and potassium hydroxide forming a liquid that can be added to pearl starch and water in a single step to form an adhesive for manufacturing corrugated paperboard.
2) Description of Related Art
Corrugated board is manufactured using starch based adhesives that typically comprise a combination of pearl starch, borax, sodium hydroxide (caustic soda), and water. The common industry practice is to individually add each of these components to a mixing unit that forms the adhesive for application by the paper corrugating machine.
In the prior art, the mixture of pearl starch, borax, sodium hydroxide and water is “cooked” to provide a final adhesive with desired viscosity, gel point and tack for application by the paper corrugating machine. A typical adhesive known in the prior art is prepared by measuring out and mixing the water, starch and sufficient sodium hydroxide to give a gel point between 130° F. and 140° F. After the first charge of starch has been gelatinized, a second charge of water is added followed by a second charge of starch, and also a charge of borax for use as a viscosity modifier and to create desired tack. The amounts of sodium hydroxide and borax measured out are important, and hence their respective ratios to each other and to the starch. Too much sodium hydroxide and the gel point of the starch is too low. Insufficient sodium hydroxide, and the gel point is too high. If the amount of borax is too low, the starch adhesive lacks tackiness, is too thin and has poor adhesion properties. If the amount of borax is too high, the starch has a heavy, stringy rheology and may be gritty.
A further problem arises in that sodium hydroxide is extremely corrosive and requires careful handling to avoid exposure to eyes and skin. In this industry, sodium hydroxide may typically be provided in a bead form in large bags that require a person to lift and dump the raw sodium hydroxide into a hopper. Alternatively, the sodium hydroxide may be provided in an aqueous solution that is manually dumped from a container into a hopper. In either form, the addition of the sodium hydroxide is a dangerous process given the nature of the material.
Additionally, borax as used in the manufacture of such starch based adhesive is typically provided as a powder or granular form in bags. In use, the bags of borax must be lifted and dumped into the hopper, during which borax can spill from the bags creating cleanup and manufacturing plant effluent issues.
Accordingly, it is an object of the present invention to provide an additive for mixing with pearl starch and water to form an adhesive for manufacturing corrugated paperboard.
It is a further object of the present invention to provide an additive in which the sodium hydroxide and borax are supplied in proper ratio to produce desirable viscosity, gel point, and tack for use in a paper corrugating machine.
It is a further object of the present invention to simplify the process of preparing starch based adhesives used in manufacturing corrugated paperboard.
It is a further object of the present invention to reduce cleanup and limit exposure risks associated with handling raw chemicals used in the manufacture of starch based adhesives.